Harpoon is by far the most successful Western anti-ship missile, over 6000 having been made. It was conceived in 1965 as an air-launched missile (a 25nm Bullpup successor), primarily to attack surfaced submarines (hence the name: a harpoon to attack whales). The main targets were Soviet submarines firing the SS-N-3 missile, which required guidance (from a surfaced submarine) well into its flight. The project began formally in 1968. Under Admiral Elmo Zumwalt, CNO from 1970 on, it was extended into a longer-range universal anti-ship missile to deal with Soviet warships, capable of being fired from standard surface ship launchers and (in encapsulated form) from submarine torpedo tubes. McDonnell Douglas (now part of Boeing) received the prime contract in June 1971. The missile was first flown on 17 October 1972. The requirement for long range (50nm) was imposed after the contract was let, a small turbojet being substituted for the rocket originally envisaged. Designations are AGM-84 for the air-launched version, RGM-84 for the ship-launched version, and UGM-84 for the submarine-launched version. In a few cases (see below) it has also been adapted for coast defense. SLAM is a modified land-attack version (see separate entry).

Additional Description:Versions: the original missiles (A/R/UGM-84A) were Block IA. They used a pop-up terminal maneuver (the missile climbs sharply about 1.8km from the target, then dives into it at an angle of 30 deg). Block IA/B missiles fly out at a set cruising altitude. The Royal Navy version of sub-Harpoon, UGM-84B, used a new sea-skimming terminal approach. Block IB (A/R/UGM-84C) for the U.S. Navy had the new sea-skimming approach and had better ECCM. Deliveries to the U.S. Navy began in June 1982. Block IC (A/R/UGM-84D) increased range by adopting JP-10 fuel (vice JP-6) and could select among terminal maneuvers. It has better ECCM and can fly several dog-legs to the target instead of the straight flight path of the earlier versions. Block IC adds the option of a high-altitude flyout (to avoid friendly ships) or can sea-skim before beginning its search. It can also make a lower-apogee pop-up attack. This version also adds a selectable search pattern (early versions were preset as narrow, medium, or wide). Production began in 1984. Earlier missiles were upgraded to Block IC at a unit cost of about $20,000. Block ID (A/RGM-84F) is lengthened to accommodate 70lb more fuel (100lbs in the earlier versions), roughly doubling aerodynamic range. The extra range allows the missile to double back and re-attack a target missed on an initial pass, flying a cloverleaf pattern. The missile\'s wings are moved forward to maintain the same angle of attack, and its guidance system is modified for maximum commonality with SLAM (AGM-84E). It incorporates a unique target identification feature. Reportedly the airframe incorporates RAM to reduce its radar signature. This version is too long to be fired from a submarine. Development began in September 1989, and Block ID first flew on 4 September 1991, and production (in the form of rebuilt Block IC missiles) was approved in 1992. Few missiles were rebuilt, due to the end of the Cold War. Blocks IE and IF are SLAMS (see separate entry). Block IG (R/UGM-84G) is a Block IC missile with Block ID guidance (re-attack capability) but without extra fuel, hence suitable for submarine use. It flies at a lower altitude than Block IC. Deliveries to international customers began in 1997.

Block II (RGM-84L, Harpoon 2000) is a next-generation missile using a SLAM guidance computer. The original radar seeker is supplemented with a GPS/INS unit adapted from that of the Boeing JDAMS. As a consequence, the missile can be used against land targets whose positions are known. This version uses surface-mounted chip technology which reduces the required number of circuit boards to five, connected by a VME bus. It has a single two-axis ring-laser gyro (as in JDAMS) in place of the two single-axis gyros of earlier versions. The mission computer uses Motorola 68040 chips. The GPS receiver is that used in SLAM-ER (AGM-84H). The radar seeker search pattern can be set to reduce land clutter effects. It uses Doppler (coherent on receive) processing to reduce the effect of land clutter and distinguish targets very close together. The missile also has a new insensitive-munitions warhead (226 kg) with a new fuze which can be set for either impact or delay. CEP is given as 10m against a land target. The initial U.S. Navy requirement is for 300 missiles (remanufactured Block IC), but ultimately about 450 are desired. However, in the event, none was bought. Other navies felt otherwise. In a unique business arrangement, Boeing funded development and the U.S. Navy paid for Block II testing. Denmark was the first customer. Late in 2001 Block II was offered to Egypt (53 missiles), but there was controversy, U.S. supporters of Israel charging that the missile would provide Egypt with a new land-attack capability. In October a possible sale of12 Block II missiles to the UAE (to arm two ex-Dutch Kortenaer-class frigates) was announced. Block II was first tested in June 2001; tests were completed in October. The first upgrade kits were delivered to Denmark in April 2002.

Denmark used missiles from scrapped ships for coast defense batteries. Spain and South Korea bought Harpoon coast defense batteries. Sub-Harpoon is operated by Australia, Egypt, Greece, Israel, Italy (which does not use the missile for surface ships), Turkey, the United Kingdom, and the United States. In addition, Canada and the Netherlands fitted submarines to fire Sub-Harpoon, but never bought any. Iran bought Harpoon, but has apparently expended the few received. Venezuela planned to buy the missile, to refit existing missile boats, but apparently the deal was not consummated. U.S. HAMILTON class Coast Guard cutters were modified to fire Harpoon, but this missile was withdrawn after the end of the Cold War. As of late 1999, the Chilean Navy was reported close to buying Harpoons (including possibly the submarine-launched version) to replace its Exocets. This purchase was not, however, made.

Range given above is approximate; the air-launched version is credited with a range as great as 120nm (about 235km). The warhead is intended to explode after penetrating, to destroy at least a single compartment. Reportedly four hits should disable a missile cruise (such as a Russian \"Kara\"), two a frigate, and one a missile boat; however, the missile has only a limited probability of sinking a target ship. Most ships carry Harpoon in two clusters of four each. The seeker is activated at a preset distance from the estimated target location. Alternatively, if only target bearing is known, the missile can be launched with its seeker activated almost immediately (bearing-rider mode).

At the Paris Air Show in 2001 the Israelis announced that they had fitted their Harpoons with a two-way Tadiran data link, making it possible to designate targets in harbors and other dense settings. Apparently the missile communicates with a helicopter, whose back-seater can see the missile\'s radar video and can lock it onto designated targets. This system presumably explains why the Israel Navy equipped some of its missile boats with helicopter platforms as long ago as 1979. Note that the link in question is NOT that of the Popeye missile. Presumably the link is part of the Harpoon Extended Performance (HEP) under development by the MBT division of IAI with U.S. support. HEP includes a new seeker and other improvements. The Israeli missile is called Harpoon II-I.

Note that U.S. Air Force F-16s based at Misawa are fitted to launch Harpoon, but it is not clear whether they ever carry it. Taiwan claimed that an April 2001 launch by one of its F-16Bs was the first-ever F-16 launch of a Harpoon missile. The missile is also carried by U.S. Navy F/A-18s and by patrol aircraft (P-3s and S-3Bs).

An upgraded Harpoon Block 21 (Harpoon III), to be developed under U.S. Navy contract, is to incorporate further Israeli modifications. Block 21 was the subject of a $3 million 8-month contract between IAI and the U.S. Navy, concluded in October 2002. By 2005 Block 21 was being called Harpoon III. This version has an improved anti-clutter radar (to detect ships near a coast or in port), with GPS (to specify aim-points and permit use for land attack), and with a data link (being developed under Air Force leadership, for a variety of U.S. weapons). As of mid-2005, the U.S. Navy wanted to begin production in FY07, but it was not clear whether money would be available. Boeing was seeking an order to upgrade up to 400 missiles. Harpoon III was cancelled, at least as a U.S. Navy program, in 2009.

As of spring 2006 Boeing was seeking a sponsor to develop a vertically-launched version of Harpoon, and it was also interested in an extended-range version. Note that a dummy vertically-launched Harpoon was tested in the prototype Mk 41 launcher.

Taiwan has a program to obtain submarine-launched Harpoon (Hai Biao, or Sea Dart); sale of such missiles was approved by the Bush Administration in April 2001. A U.S. review (2004) suggested deferring Sea Dart until an appropriate means of target acquisition became available, in the form of a submarine terminal for the indigenous Link T.

In August 2009 the U.S. government charged that Pakistan was converting Harpoons (of which it was provided 165) into land-attack missiles to be delivered by ships and P-3C aircraft, in contravention of end-use agreements. The Pakistanis tested a missile on 23 April 2009 which the U.S. government identified as a modified Harpoon. The Pakistanis responded that it was their own development, perhaps a modified reverse-engineered version of Harpoon. The dispute arose as Congress took up a $7.5 billion aid package, and as the Obama Administration tried to divert Pakistani energies from counters to India towards anti-terrorist efforts.

In September 2010 an Indian order for $170 million worth of Harpoon II missiles was formally concluded; it had first been announed during a 2008 visit to Washington by the Indian defense minister. The order does not apply to the Indian version of the P-8 maritime patrol aircraft, details of which are still being finalized. That suggests that the Indians see Harpoon II as a preferable alternative to the Russian-supplied Kh-35, which is roughly equivalent. Harpoon II offers land- as well as ship-attack options, using GPS, which the Russian missile lacks.

In June 2012, India announced that the Ministry of Defense was negotiating the sale of UGM-84 issiles to equip 4 German-built Shishumar Type 209/1500 class diesel electric submarines.

In November 2015, the USN completed the first free-flight test of the AGM-84N Harpoon Bk II+ air-launched ASM. The new weapon is a modified version of the original Harpoon that has the capability to receive in-flight updates to allow the engagement of high-speed maneuvering targets.

In April 2016, the Royal Canadian Navy (RCN) conducted the first test of an RGM-84L Harpoon Block II from the HMCS Vancouver at a shore-based target. This marks the first test of its kind for the RCN, having never had a land attack capability in the past.

In November 2016, the Royal Navy (RN) announced that it would withdraw the GWS 60 HArpoon Block IC missiles from serive in 2018. This will leave the RN without a long-range anti-ship missile capability.